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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made October 20, 2017

 Days 3-7Days 8-14Prob. Days 8-14
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Categorical Outlooks
Experimental Probabilistic Outlooks (Information)

Valid Monday October 23, 2017 to Friday November 03, 2017

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT October 20 2017

Synopsis: A cold front is anticipated to sweep across the eastern half of the Contiguous U.S. early in the day 3 to 7 period, with a reinforcing shot of colder air later next week. High pressure is forecast to build in across the West early next week, only to be dislodged by the second cold front, with high pressure behind that front building southward from Canada. A strong low-pressure system is forecast to impact western and southern Alaska during next week, with more extended impacts to western Alaska. Some models favor low-pressure across the eastern contiguous U.S. during week-2, but model solutions exhibit increased uncertainty.

Hazards Detailed Summary

For Monday October 23 - Friday October 27: A cold front is forecast to push across the eastern CONUS during next week, with a wave of low-pressure moving from south to north along the front. This wave of low-pressure is expected to support heavy rains (up to 4.0 inches in 48 hours) across portions of the Tennessee Valley. Some isolated severe weather is possible from the Southern Great Plains to the Lower Mississippi Valley, likely in the form of a squall line, on Sunday. As the low-pressure system moves northward, heavy rains are forecast to spread to the Mid-Atlantic and Northeast. Some models indicate wind speeds approaching 30 mph near the Northeast coast, later on Tuesday and into Wednesday, Oct 25, though model uncertainty in the wind speeds is too high to depict a hazard.

High pressure is likely to build over the Rockies, in a position where a high pressure system can support high winds over California. The strong winds are likely to contribute to critical fire weather conditions over southern California on Oct 23-24, with marginal fire weather conditions extending to the 24th. During Mon-Tue, Oct 23-24, strong winds (greater than 35 mph) are also forecast over the northern and Central Plains on the northern periphery of the high pressure system.

A second cold front is forecast to move southward over the Great Plains later next week. Some upslope flow is possible in Montana and Wyoming, leading to locally moderate snows, though the moisture supply will be limited, restricting potential snowfall totals. WPC and your local WFO will have the latest information on that scenario.

Multiple low-pressure systems are forecast to impact Alaska. High winds (exceeding 40 mph), high significant wave heights, and heavy precipitation are likely for Southeast Alaska and the Alaska Panhandle early next week, Mon-Tue, with the first system. A subsequent low-pressure system is forecast to develop near the Aleutians, and track eastward toward southern coastal Alaska, spreading heavy precipitation (exceeding 3 inches in 24 hours), high winds (likely in excess of 50 mph in some locations), and high significant wave heights. The second round of impacts are likely to begin on Oct 24, and spread eastward, while lasting through Oct 27.

For Saturday October 28 - Friday November 03: There is good agreement between the 6Z GEFS and 0Z ECMWF Ensemble regarding the development of a mid-level trough across the eastern half of the CONUS for the early portion of Week-2, then disagreement and uncertainty increase quickly. This pattern may translate to much below normal temperatures across the eastern half of the CONUS Oct 28 to 29. Models indicate a transition to a more zonal flow for the rest of week-2. The GEFS Reforecast Tool indicates a 40 percent chance of temperatures reaching the lowest 15th percentile in the area highlighted as a moderate risk, with the minimum temperatures of some areas reaching sub-freezing temperatures. This cold event could be the first freeze for portions of the Ohio Valley and Corn belt.

An amplified mid-level ridge is predicted to build across the western half of the CONUS at the beginning of week-2. This pattern favors a slight chance of much above normal temperatures across parts of southern California and the Southwest, Oct 28. The GEFS Reforecast Tool indicates a 20 percent chance or greater of maximum temperatures in the highlighted areas reaching the 85th percentile and localized areas reaching up to 90 deg F.

The U.S. Drought Monitor, valid on October 10, indicates that severe to exceptional (D2-D4) drought covers 2.98 percent of the continental U.S., down from 4.03 percent of the CONUS. The largest changes were over the Northern Plains and Midwest.

Forecaster: Matthew Rosencrans


Click here to see a display of the GFS Ensemble Forecasts

Please consult local NWS Forecast Offices for short range forecasts and region-specific information.